Conventional land vehicles include a frame with axles and multiple wheels. The frame is suspended from the axle and wheel assemblies at a given ride height, i.e. ground clearance. Traditionally the ride height of a vehicle is fixed. However, adjustable ride height systems allow for the ride height of a vehicle to be altered.
The ability to adjust the ride height of a land vehicle provides several advantages. Increasing the ride height allows a vehicle to travel over more significant obstacles, e.g. rocks, bumps, downed trees, streams, and other irregularities in the surface over which the vehicle is traveling. An increased ride height also allows a vehicle to operate with larger tires for enhanced off road capability. Decreasing the ride height of a vehicle provides a lower roll center for increased stability and cornering capability, which may be desired for high speed travel over smooth surfaces.
Unfortunately, traditional systems used to adjust the ride height of a vehicle suffer from a limited amount of ride height adjustment capability without significant effort. Additionally, traditional systems used to adjust ride height result in detrimental effects to ride quality, wheel positioning, and/or steering alignment.
To demonstrate these deficiencies, a prior art vehicle 100, typical of a commercially available pickup truck, is illustrated in FIG. 1. The vehicle 100 is comprised of a body 101 attached to a frame 105. The vehicle 100 has a total of four wheels 110, two of which are attached to a straight axle 115 in the front, and two of which are attached to a straight axle 115 in the rear. The wheel 110 is permitted to rotate around the centerline of the straight axle 115, allowing the vehicle 100 to travel over the surface 200. The straight axle 115 illustrated in the rear of the vehicle 100 is positioned beneath the frame 105 via a traditional leaf spring suspension 300. The straight axle 115 illustrated in the front of the vehicle 100 is positioned beneath the frame 105 via a multi-link suspension 400.
The leaf spring suspension 300 and the multi-link suspension 400 are two exemplary prior art ways to position the straight axles 115 relative to the frame 105, support the sprung weight, i.e. the weight of the frame 105, body 101, and passengers/cargo, and provide dampening as the vehicle 100 travels over bumps in the surface 200.
Referring first to the rear of the exemplary vehicle 100 illustrated in FIG. 1, the leaf spring suspension 300 comprises a leaf spring pack 305, pivotally attached to the frame 105 in the front, pivotally attached to a spring shackle 310 in the rear, and bolted to the straight axle 115 via a short lift block 315 which provides the interface surface between the bottom center of the leaf spring pack 305 and the straight axle 115. The spring shackle 310 is pivotally attached to the frame 105, allowing the leaf spring pack 305 to compress or expand as the vehicle 100 travels over bumps in the surface 200. The leaf spring pack 305 performs the function of positioning the straight axle 115 in the front to rear direction, supporting the sprung weight, and establishing the fixed ride height H. The shock 320 is pivotally attached to the frame 105 and the straight axle 115, and provides the dampening function.
Referring now to the front of the exemplary vehicle 100 illustrated in FIG. 1, the multi-link suspension 400 comprises a shock tower 405 fixed to the frame 105. A coilover 410, which comprises a coil spring and a shock, is pivotally attached to the shock tower 405 and pivotally attached to the housing of the straight axle 115. The coilover 410 supports the sprung weight, establishes the ride height H, and provides dampening, but does not position the straight axle 115 in the front to back direction. Alternatively, a separate coil spring and shock, or an air spring and shock may be used in lieu of the coilover 410. The straight axle 115 is positioned front to back by the links 415 which are pivotally attached to the housing of the straight axle 115 and pivotally attached to the frame link mount 420. A coilover 410 may provide a small amount of adjustability to the ride height H (typically 2-4 inches). However, this limited amount of adjustability may not satisfy that which is required for traversing significant obstacles on the surface 200.
Traditional means of adjusting the ride height H are illustrated in FIG. 2 for both the leaf spring suspension 300 and the multi-link suspension 400. In FIG. 2, the ride height H has been increased approximately 13″ from that shown in FIG. 1.
With regards to the leaf spring suspension 300 in the rear, the increase in ride height H may be accomplished by substituting the short lift block 315 with a tall lift block 316 and the shock 320 with a long shock 321. This method results in what is known in the art as “axle wrap” due to the longer moment arm created between the base of the leaf spring pack 305 and the surface 200, and requires significant time to alter the ride height. Another traditional means of increasing the ride height H as illustrated in FIG. 2 is to install a large leaf spring pack 306. The large leaf spring pack 306 reduces and/or eliminates the “axle wrap”, but typically creates a harsher ride quality than the original leaf spring pack 305 due to the increased spring constant as a result of the increased convexity and/or number of leaves making up the pack. The large leaf spring pack 306 still requires a long shock 321 and significant effort to change the ride height H.
With regards to the multi-link suspension 400 in the front, the increase in ride height H can be accomplished by substituting the coilover 410 with a longer coilover 411. The longer coilover 411 can be expensive, and this substitution requires significant time. Also, since the links 415 travel in an arc, the wheelbase W is shortened as the ride height H is increased, requiring the links 415 to be lengthened to compensate.
FIGS. 3A and 3B each illustrate the front view of the exemplary vehicle 100, depicting a traditional panhard bar 425 pivotally attached to the frame 105 and pivotally attached to the straight axle 115. The traditional panhard bar 425 positions the straight axle 115 in the left to right position relative to the frame 105. As illustrated in FIG. 3B, as the ride height H is increased, the body 101 moves to the side as a result of the traditional panhard bar 425 traveling in an arc. Although the front view of the multi-link suspension 400 is shown, a traditional panhard bar is also used in the same manner as a component of the leaf spring suspension system 300 in the rear of the exemplary vehicle 100.
FIG. 4 illustrates the exemplary vehicle 100 steering system 500 as traditionally used in conjunction with a straight axle 115. The steering system 500 comprises a drag link 505 which is attached at one end via a ball and socket joint to the pitman arm 510 and at the other end via a ball and socket joint to the steering tie bar 515. The steering tie bar 515 is attached at both ends to the spindles 520 via a ball and socket joint (note: in some applications the drag link 505 attaches directly to one of the spindles 520). As the pitman arm 510 translates left and right, the spindles 520 are turned left and right, thus steering the vehicle 100 as illustrated in FIG. 5A (centered), FIG. 5B (turning right), and FIG. 5C (turning left).
The traditional steering system 500 illustrated in FIG. 6 is shown at the lower ride height H. At this specific ride height H, the traditional steering system 500 is effective since the drag link 505 is adjusted to permit the pitman arm 510 to be centered in its travel from left to right, and the angle ω between the drag link 505 and the surface 200 is small. However, as shown in FIG. 7, the traditional steering system 500 suffers limitations as the ride height H of the vehicle is altered. Increasing the ride height H increases the angle ω, which exacerbates what is known in the art as “bump steer.” “Bump steer” is a result of the drag link 505 traveling in an arc as the straight axle 115 moves vertical relative to the frame 105. This vertical motion is a result of the vehicle 100 traveling over irregularities in the surface 200. As further illustrated in FIG. 7, changing the ride height H causes the pitman arm 510 to rotate, which causes steering misalignment unless the length of the drag link 505 is adjusted via a replacement drag link to compensate.
As such, there is a need for a system that can be used to adjust the ride height of a vehicle without significant effort, and without significant impacts to the ride quality, wheel positioning, or the steering alignment of a vehicle